Four fire engines and around 25 firefighters dealt with flooding on Wealdstone High Street.
A 24-inch water main burst, causing flooding up to a depth of around 30cm in the area from Locket Road to Masons Avenue. Around 10 shops were affected by flood water. Crews used sandbags at the scene to protect further properties from damage and worked to divert flood water.
Station Commander Chris Swallow said: "There were road closures in place between Ellen Webb Drive and College Avenue whilst firefighters worked with partners to make the scene safe.
"We urged people to avoid the area where possible."
The Brigade was called at 0626 and the incident was over for firefighters by 1045. Fire crews from Harrow, Stanmore and Northolt fire stations attended the scene.